Coherence and wavefront characterization of Si-111 monochromators using double-grating interferometry.

Area of Science:

• X-ray optics
• Coherent X-ray imaging
• Synchrotron radiation instrumentation

Background:

• Monochromators are essential for selecting specific X-ray wavelengths in experiments.
• Coherence and wavefront properties of X-ray beams are critical for high-resolution imaging.
• Previous studies have focused on various monochromator designs, but direct comparison of coherence properties is limited.

Purpose of the Study:

• To compare the coherence and wavefront properties of a pseudo-channel-cut monochromator against a double-crystal monochromator.
• To analyze wavefront distortions introduced by these monochromators and other optical elements.
• To assess the suitability of these monochromators for hard X-ray coherent diffraction imaging.

Main Methods:

• Utilized a double-grating interferometer specifically designed for hard X-ray applications.
• Measured the complex coherence factor of the X-ray beam.
• Quantified wavefront distortions at the sample position after various optical elements.

Main Results:

• The pseudo-channel-cut monochromator exhibited a transverse coherence length in the vertical direction that was twice as large as that of the double-crystal monochromator.
• This enhanced coherence is attributed to the superior mechanical stability of the channel-cut design.
• Wavefront distortions introduced by different optical elements, including monochromators and mirrors, were successfully quantified.

Conclusions:

• The pseudo-channel-cut monochromator demonstrates significantly improved coherence properties compared to the double-crystal monochromator.
• Its higher mechanical stability directly translates to better beam coherence, essential for coherent imaging.
• This study provides valuable insights for selecting appropriate monochromators in synchrotron-based coherent diffraction imaging.